# SXMicrocontrollerMathMethod

## Divide 16 bit int by 8 bit int to 8 bit int and remainder

by Lou Zher

```;-[ Div ]--------------------------------------------------------------
;	call	w/: Number in f_divhi:f_divlo
; Returns: Quotient in f_divlo, remainder in f_divhi. W preserved.
;          Carry set if error. Z if divide by zero, NZ if divide overflow.
; Notes:   Works by left shifted subtraction.
;          Size = 29, Speed(w/ call&ret) = 9 cycles if div by zero
;          Speed = 104 minimum, 142 maximum cycles
;          Not compatible with the CARRYX option.

Div
or	W, #0		; w |= 0 (to test for div by zero)
setb	C		; set carry in case of error
snb	Z		; if zero
ret			;   return (error C,Z)

call	DivSkipHiShift
call	DivCode
call	DivCode
call	DivCode
call	DivCode

call	DivCode
call	DivCode
call	DivCode
call	DivCode

rl	f_divlo		; C << lo << C

; If the first subtract didn't underflow, and the carry was shifted
; into the quotient, then it will be shifted back off the end by this
; last RLF. This will automatically raise carry to indicate an error.
; The divide will be accurate to quotients of 9-bits, but past that
; the quotient and remainder will be bogus and carry will be set.

clrb	Z		; NZ (in case of overflow error)
ret			; we are done!

DivCode
rl	f_divlo		; C << lo << C
rl	f_divhi		; C << hi << C
sb	C		; if Carry
jmp	DivSkipHiShift	;
sub	f_divhi, W	;   hi-=w
setb	C		;   ignore carry
ret			;   done
; endif
DivSkipHiShift
sub	f_divhi, W	; hi-=w
snb	C		; if carry set
ret			;   done
clrb	C		; clear carry
ret			; done

```

• This algorithm is fine, but the original listing was missing a
call DivCode
for 8 bit divisors+. That has now been added.

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